1. Field
Embodiments of the present disclosure relate to measurement of geometrical parameters of threaded connections and for assessing the quality of a coating deposition process. The disclosed embodiments are especially suited for threaded pipes used in the hydrocarbon industry and for similar threaded objects.
2. Description of the Related Art
Oil and gas pipe connections may be prepared with dry coatings in order to avoid the use of dopes and attendant drawbacks. For example, documents EP 1554518, EP 1954953, and EP 2102542, the entirety of each of which are incorporated by reference, disclose threaded joints where all or part of the threading is covered with dry coating.
Generally, dry coatings are applied after performing a threading operation of pipe ends. The dry coatings are designed to provide both high galling resistance during make up operations in the oil field and high corrosion resistance. Corrosion resistance is desirable during transport and storage of the pipes so as to inhibit damage to the pipes.
During manufacturing of threads in products such as screws, bolts, and threaded pipes, it is beneficial to verify that the geometrical dimensions of these pieces complies with tolerances set for the product. In addition, knowledge of the nature of the deviation from these tolerances can be used for feedback to the manufacturing process, allowing for the production of fewer products having geometrical dimensions outside of the tolerances.
A difficulty encountered in performing measurement operations on threaded products is the precision and repeatability of the measurements. In this particular technical field, several parameters are typically measured, such as taper of the pin and the box, the thread pitch, the thread height, the diameter of the pin or box, the pipe ovality, and run in and run out. In the past, there have been attempts to improve accuracy and repeatability of measurement operations and to fabricate measurement systems capable of measuring the thread shape of complex mechanical objects such as pipe threads used in the oil industry.
For example, U.S. Pat. No. 5,712,706 discloses a non-contact, laser-based sensor that is guided by a precision mechanical system. The system scans a thread profile and produces a set of computer images of the threading. The computer images are then analyzed to acquire quantitative information about characteristics of the threads, such as pitch, lead, root radius, flank angle, surface roughness, helix variation, and pitch diameter. However, U.S. Pat. No. 5,712,706 does not explicitly address explicitly the issue of piece misalignment. As a result, high precision is needed when aligning the piece to be measured with the mechanical system coordinates. This alignment can be conventionally achieved when the piece is at the threading machine.
Unfortunately, performing measurements at the threading machine has several disadvantages. In one aspect, performing measurements at the threading machine adds costly time to the threading process by inhibiting inspection and manufacturing from being performed at the same time. Instead, performing measurements at the threading machine entails placing delicate optics and precise mechanical components in a hostile environment (e.g., cutting oil and strong vibrations present). Further, when performing measurements at the threading machine the same mechanical movement that has to be verified is used, to some extent. Once the piece has been removed from the lathe, this alignment is very difficult to achieve manually. Consequently, the system disclosed by U.S. Pat. No. 5,712,706 only allows measurement of relative or local magnitudes (i.e. thread height by comparing contiguous crests and roots). Measurement errors introduced by a piece misalignment are not “noticed” according to U.S. Pat. No. 5,712,706, and in these cases produces an insufficiently precise measurement.
Furthermore, U.S. Pat. No. 5,712,706 does not address the measurement of thread parameters such as taper, run-in, run-out, black crest, length of complete thread. Specific process parameters, such as taper profile, pitch linearity, Fourier mode decomposition of ovality, lathe plate misalignment, hook end angle severity, are also not addressed.
In case where a coating is applied to the pipe threading (e.g., a dry lubricant), additional problems are encountered. As in the case of non-coated pipes, it is beneficial to ensure and verify the geometrical dimensions of the finished piece after the coating process so that tolerances set for the final product with the threading may be satisfied. In addition, the information on the nature of the deviation from these tolerances may be used as a feedback on the manufacturing process, allowing for the production of fewer products having geometrical dimensions outside of the tolerances.
Another difficulty encountered in performing measurement operations on coated joints is an inability to ensure that the coating material is not damaged during the measurement procedure (e.g., due to handling of the pipes and/or to the use of contact type measuring devices).
While measuring systems have been proposed for measuring coatings in general and measurement of coating applied on tubular products, none of these measurement systems is adapted to measurement of dry coatings applied on threaded parts of tubular joints.
In one example, a measurement technique employing ultrasound is known, however, it cannot be applied to coatings as thin as those applied in threaded joints for the hydrocarbon industry, since the wavelength of ultrasound is much larger than the thicknesses to be measured.
In another example, a measurement technique using eddy currents is known, however, this technique requires that the measurement device is placed either in contact or very close to the work piece. Because of the complex geometry and generation of boundary effects, it is difficult to use this technique on threaded parts of joints. The deformation of field lines because of the geometry and the fact that the sensor must be very near to the thread surface are two important constraints.
In a further example, a measurement technique based on X-ray fluorescence or back scattering is known where the coating highlights when it is irradiated and the fluorescence is reabsorbed by the coating. The amount of fluorescence measured is proportional to the thickness and the results are influenced by several factors. It is not a technique generally applicable and, in complex cases, the results depend on the angle of incidence of X-rays. Another drawback is the use of X-rays which are harmful to operators.
In an additional example, a measurement technique based on infrared (IR) absorption is known, where excitation of the coating is made by visible light. The application of this technique depends upon whether the coating is made of a material which is excitable by light and upon the grade of IR absorption.
Therefore, a need exists for measurement devices and methods that provide measurement of threaded products that are repeatable, satisfactory, and precise manner.